Light generating microcapsules for photo-curing

ABSTRACT

A process of curing a photo-curable material includes dispersing a microcapsule in a material that includes a photo-initiator and a photo-curable material. The process also includes applying a stimulus to the microcapsule to trigger a chemiluminescent reaction within the microcapsule. The chemiluminescent reaction generating a photon having a wavelength within a particular emission range that is consistent with an absorption range of the photo-initiator. The photon exits the microcapsule to trigger the photo-initiator to initiate or catalyze curing of the photo-curable material.

BACKGROUND

Some polymers and adhesives are capable of being cured via exposure to alight source, such as an ultraviolet (UV) light source. A disadvantageassociated with such a curing method is that the UV radiation enters thepolymer/adhesive from an outer surface. As such, full curing of thepolymer/adhesive may occur at the surface, but curing may decrease alonga depth of the polymer/adhesive as a result of absorption of the UVradiation, resulting in a partially cured polymer/adhesive. In order tofully cure the polymer/adhesive, other means are employed such asthermal curing.

SUMMARY

According to an embodiment, a process of curing a photo-curable materialis disclosed. The process includes dispersing a microcapsule in amaterial that includes a photo-initiator and a photo-curable material.The process also includes applying a stimulus to the microcapsule totrigger a chemiluminescent reaction within the microcapsule. Thechemiluminescent reaction generating a photon having a wavelength withina particular emission range that is consistent with an absorption rangeof the photo-initiator. The photon exits the microcapsule to trigger thephoto-initiator to initiate or catalyze curing of the photo-curablematerial.

According to another embodiment, an in-situ photo-curing process isdisclosed. The process includes forming an assembly that includes amaterial disposed between a first component and a second component. Thematerial includes a photo-initiator, a photo-curable material, andmicrocapsules dispersed therein. The process also includes applying astimulus to the assembly that triggers chemiluminescent reactions withinthe microcapsules. The chemiluminescent reactions generate photonshaving wavelengths within a particular emission range that is consistentwith an absorption range of the photo-initiator. The photons exit themicrocapsules for in-situ curing of the photo-curable material.

According to another embodiment, a material is disclosed that includes aphoto-initiator, a photo-curable material, and a microcapsule. Themicrocapsule includes a first compartment that contains a firstreactant. The microcapsule also includes a second compartment thatcontains a second reactant. The microcapsule also includes an isolatingstructure separating the first compartment from the second compartmentand is adapted to rupture in response to application of a stimulus tocause the first reactant and the second reactant to undergo achemiluminescent reaction. The chemiluminescent reaction generates aphoton having a wavelength within a particular emission range that isconsistent with an absorption range of the photo-initiator. The photonexits the microcapsule to trigger the photo-initiator to initiate orcatalyze curing of the photo-curable material.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of exemplary embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a cross-sectional view of an assemblythat includes multiple-compartment microcapsules dispersed in aninterface material that includes a photo-initiator and a polymericmaterial that is cross-linkable, according to one embodiment. In FIG. 1,an individual microcapsule is depicted in an exploded cross-sectionalview prior to application of a stimulus to cause a chemiluminescentreaction with a photon emission wavelength that is satisfactory totrigger the photo-initiator to cross-link the polymeric material.

FIG. 2 is a diagram illustrating a cross-sectional view of the assemblydepicted in FIG. 1 after application of the stimulus to cause thechemiluminescence reaction, according to one embodiment. In FIG. 2, anindividual microcapsule is depicted in an exploded cross-sectional viewto show that a substantial portion of the photons generated within themicrocapsule may be transmitted into the interface material in order totrigger the photo-initiator to cross-link the polymeric material.

FIG. 3A is a diagram illustrating a multiple-compartment microcapsulehaving a shell-in-shell architecture with an inner shell containedwithin an outer shell, according to one embodiment. The inner shell isadapted to rupture in response to application of a compressive force inorder to trigger a chemiluminescent reaction, according to oneembodiment.

FIG. 3B is a diagram illustrating a multiple-compartment microcapsulehaving an inner barrier to form compartments, according to oneembodiment. The inner barrier is adapted to rupture in response toapplication of a compressive force in order to trigger achemiluminescent reaction, according to one embodiment.

FIG. 4 is diagram illustrating a process of forming an electroniccomponent cooling assembly having a cross-linked thermal interfacematerial by applying a compressive force to an assembly including athermal interface material disposed between a heat generating componentand a heat dissipating component, according to one embodiment. FIG. 4illustrates that application of the compressive force causes achemiluminescent reaction with a photon emission wavelength that issatisfactory to form the cross-linked thermal interface material.

FIG. 5 is a flow diagram illustrating a method of producing amultiple-compartment microcapsule having a shell-in-shell architecturewith an inner shell contained within an outer shell, where the innershell is adapted to rupture in response to application of a compressiveforce to cause a chemiluminescent reaction within the microcapsule,according to some embodiments.

DETAILED DESCRIPTION

The present disclosure describes light generating microcapsules andprocesses of utilizing the light generating microcapsules for in-situgeneration of light within a polymer/adhesive for curing/cross-linkingof the polymer/adhesive. Chemiluminescence is the emission of photons asthe result of a chemical reaction. In the present disclosure, amicrocapsule includes multiple compartments to isolate a first reactant(or a first set of reactants) from a second reactant (or a second set ofreactants) within the same microcapsule. Application of a particularstimulus (e.g., a compressive force, heat, or a combination thereof) tothe microcapsule results in rupture of an inner compartment, enablingthe first reactant(s) and the second reactant(s) to mix and undergo achemiluminescent reaction within the microcapsule.

The microcapsules of the present disclosure may be dispersed within apolymer/adhesive (e.g., a thermal interface material) that includes aphoto-initiator and photo-curable cross-linkers. An outer shell of themicrocapsule may be formed from a material that enables a substantialportion of the light generated within the microcapsule to exit themicrocapsule into the surrounding polymer/adhesive. The in-situgeneration of light within the polymer/adhesive may trigger thephoto-initiator to initiate or catalyze the curing of the photo-curablecross-linkers. Thus, in contrast to existing techniques of curing apolymer/adhesive by exposing an outer surface of the polymer/adhesive toa light source (e.g., a UV light source), the in-situ generation oflight by the microcapsules of the present disclosure that are dispersedwithin the polymer/adhesive enable the polymer/adhesive to be fullycured without employing other means, such as thermal cycling.

As used herein, the term “light” is used to refer to ultraviolet (UV)light (in a wavelength range of 10 nm to 400 nm), visible light (e.g.,in a wavelength range of 400 nm to 700 nm), or infrared light (e.g.,above 700 nm) that may be produced as a result of a chemiluminescentreaction. As used herein, the term “microcapsule” is used to refer tocapsules that are in a range of about 10 microns to 1000 microns indiameter. However, it will be appreciated that the following disclosuremay be applied to capsules having a smaller size (also referred to as“nanocapsules”).

Referring to FIG. 1, a diagram 100 illustrates a cross-sectional view ofa particular embodiment of an assembly 102 that includes a plurality ofmicrocapsules 104 dispersed in an interface material 106. Themicrocapsules 104 illustrated in FIG. 1 include multiple compartmentsand are also referred to herein as multiple-compartment microcapsules orlight generating microcapsules. In FIG. 1, the interface material 106further includes a photo-initiator and a polymeric material havingcross-linking moieties that are triggered using light (also referred toherein as “photo-curable cross-linkers”). In FIG. 1, the microcapsules104 are shown prior to application of a particular stimulus (e.g., acompressive force, heat, or a combination thereof) that results in achemiluminescent reaction within the individual microcapsules 104.Accordingly, FIG. 1 illustrates that the compartments of themicrocapsules 104 enable isolation of reactants in order to prevent thechemiluminescent reaction prior to application of the particularstimulus.

FIG. 1 illustrates an example in which the interface material 106defines an interface between a first component 108 and a secondcomponent 110. In a particular embodiment, the interface material 106corresponds to a thermal interface material that is compressed betweenthe first component 108 and the second component 110, filling gapsassociated with irregularities in a first mating surface 112 of thefirst component 108 and a second mating surface 114 of the secondcomponent 110. In some cases, as illustrated and further describedherein with respect to the example of FIG. 4, the first component 108 ofFIG. 1 may correspond to a heat spreader surrounding an electroniccomponent that generates heat during operation, the second component 110may correspond to a heat dissipating component (e.g., a heat sink orcold plate), and the interface material 106 may enable efficient heattransfer from the first component 108 to the second component 110. Inalternative embodiments, the microcapsules 104 depicted in FIG. 1 may bedispersed in a photo-curable adhesive.

The photo-curable material in the interface material 106 may correspondto an epoxy-based material, an acrylate-based material, or another typeof photo-curable material that is “tuned” to the radiation resultingfrom a particular chemiluminescent reaction. A photo-curable materialbegins to cure as its photo-initiator is energized by radiation from achemiluminescent light source. As an example, a photo-curablemethacrylate material may be “tuned” to respond to different wavelengthsof light depending on the particular photo-initiator that is used. Asanother example, a photo-curable epoxy material may be “tuned” torespond to different wavelengths of light depending on the particularphoto-initiator that is used.

In the particular embodiment depicted in FIG. 1, the microcapsules 104dispersed in the interface material 106 have a shell-in-shellarchitecture with an inner shell contained within an outer shell, wherethe inner shell is adapted to rupture in response to application of astimulus (e.g., a compressive force and optionally heat) in order totrigger a chemiluminescent reaction within the microcapsules 104. Thus,the individual microcapsules 104 may correspond to themultiple-compartment microcapsule 300 depicted in FIG. 3A (having theshell-in-shell architecture). Alternatively, the individualmicrocapsules 104 of FIG. 1 may correspond to the multiple-compartmentmicrocapsule 310 depicted in FIG. 3B. It will be appreciated that, inalternative embodiments, the microcapsules 104 of FIG. 1 may have analternative multiple-compartment microcapsule design, may include morethan one type of multiple-compartment microcapsule design, or acombination thereof.

FIG. 1 further includes an exploded cross-sectional view of anindividual microcapsule 120 of the plurality of microcapsules 104 priorto application of a particular stimulus (e.g., a compressive force andoptionally heat for the microcapsule design depicted in FIG. 1). Theexploded cross-sectional view illustrates that the microcapsule 120 hasan outer wall 122 (also referred to herein as the “outer shell”) andcontains an inner microcapsule 124 and a first reactant 126 (or a firstset of multiple reactants). The inner microcapsule 124 has a capsulewall 128 (also referred to herein as the “inner shell”) and contains asecond reactant 130 (or a second set of multiple reactants). The firstreactant(s) 126 within the microcapsule 120 may surround the innermicrocapsule 124, and the first reactant(s) 126 may be prevented fromcontacting the second reactant(s) 130 by the capsule wall 128 of theinner microcapsule 124.

As illustrated and further described herein, subsequent application of astimulus to the microcapsules 104 may result in rupture of the capsulewall 128 of the inner microcapsule 124, allowing the first reactant(s)126 and the second reactant(s) 130 to mix and undergo a chemiluminescentreaction. As described further herein, an example of a chemiluminescentreaction is the reaction of a suitable dye with diphenyl oxalate and asuitable oxidant such as hydrogen peroxide to produce a photon-emittingreaction. To illustrate, in some cases, the first reactant(s) 126 maycorrespond to hydrogen peroxide, and the second reactant(s) 130 maycorrespond to a mixture of a dye and diphenyl oxalate. As illustratedand described further herein with respect to FIG. 4, a product of achemical reaction between diphenyl oxalate and hydrogen peroxide is1,2-dioxetanedione that has an unstable strained ring, which decomposesspontaneously to carbon dioxide and releases energy that excites a dye,and the excited dye subsequently releases a photon as it returns to itsground state.

In the particular embodiment depicted in FIG. 1, the stimulus that issubsequently applied to the microcapsules 104 corresponds to acompressive force (and optionally heat). In this case, the capsule wall128 of the inner microcapsule 124 may be formed to rupture under aparticular compressive force, and the outer wall 122 of the microcapsule120 may be formed so as to not rupture under that compressive force.

As described further herein, the chemiluminescent reaction generatesactinic photons within a particular wavelength range that issatisfactory to trigger the particular photo-initiator to initiate orcatalyze the curing of the photo-curable material in the interfacematerial 106. The outer wall 122 of the microcapsule 120 allows asubstantial portion of the actinic photons generated within themicrocapsule 120 as a result of the chemiluminescent reaction to passthrough the outer wall 122 into the surrounding interface material 106.The outer wall 122 can be made from chemically non-reactive materials,such as some plastics which are transparent, translucent, or lightfiltering to pass the curing wavelengths of light from chemiluminescentlight source into the interface material 106. In an embodiment, theouter wall 122 has a transmittance value of at least 90% for theparticular emitted photon wavelength(s). In certain embodiments, theouter wall 122 may include a natural polymeric material, such asgelatin, arabic gum, shellac, lac, starch, dextrin, wax, rosin, sodiumalginate, zein, and the like; semi-synthetic polymer material, such asmethyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethylethyl cellulose; full-synthetic polymer material, such as polyolefins,polystyrenes, polyethers, polyureas, polyethylene glycol, polyamide,polyurethane, polyacrylate, epoxy resins, among others.

Thus, FIG. 1 illustrates an example of an assembly that includes lightgenerating microcapsules dispersed in an interface material (e.g., athermal interface material, an adhesive, etc.) that includes aphoto-initiator and a photo-curable material. In FIG. 1, themicrocapsules are shown prior to application of a stimulus to themicrocapsules. Accordingly, the compartment(s) of the microcapsulesisolate reactants that undergo a chemiluminescent reaction. As describedfurther herein with respect to FIGS. 2 and 4, applying a stimulus (e.g.,a compressive force and optionally heat) to the microcapsules results inrupture of the capsule wall of the inner microcapsule, allowing thereactants to mix and undergo the chemiluminescent reaction.

Referring to FIG. 2, a diagram 200 illustrates a cross-sectional view ofthe assembly 102 depicted in FIG. 1 after application of a particularstimulus to the microcapsules 104, according to one embodiment. FIG. 2illustrates that application of the particular stimulus (e.g., acompressive force and optionally heat for the microcapsule designdepicted in FIG. 1) results in a chemiluminescent reaction within theindividual microcapsules 104.

In FIG. 2, an exploded cross-sectional view illustrates the individualmicrocapsule 120 of FIG. 1 after application of a particular compressiveforce to the microcapsules 104 dispersed in the interface material 106.FIG. 2 illustrates that application of the stimulus to the microcapsules104 results in rupture of the capsule wall 128 of the inner microcapsule124 depicted in FIG. 1 to allow the first reactant(s) 126 and the secondreactant(s) 130 to mix and undergo a chemiluminescent reaction(identified by the reference character 202 in FIG. 2). FIG. 2 furtherillustrates that application of the particular compressive force doesnot result in rupture of the outer wall 122 of the microcapsule 120.

FIG. 2 illustrates that the chemiluminescent reaction 202 that occurswithin the microcapsule 120 generates light 204 (identified as “hv” inFIG. 2), and the outer wall 122 of the microcapsule 120 allows asubstantial portion of the light 204 (or particular curing wavelength(s)of the light 204) to pass through the outer wall 122 into thesurrounding interface material 106. As described further herein, thelight 204 is within a particular wavelength range that is satisfactoryto trigger a particular photo-initiator to initiate or catalyze thecuring of the photo-curable material in the interface material 106. FIG.2 further illustrates that the microcapsule 120 may contain a reactionproduct 206 of the reaction of the first reactant(s) 126 and the secondreactant(s) 130. As the outer wall 122 remains intact after applicationof the particular compressive force, the outer wall 122 may prevent thereaction product 206 from contacting the interface material 106.

Thus, FIG. 2 illustrates that application of a stimulus to themicrocapsules causes a chemiluminescence reaction to occur within themicrocapsules. FIG. 2 further illustrates that a substantial portion ofthe photons generated within the microcapsules may be transmitted into asurrounding material in order to trigger the photo-initiator thatinitiates or catalyzes the curing of a photo-curable material in thesurrounding material.

FIG. 3A is a diagram illustrating a cross-sectional view of amultiple-compartment microcapsule 300 having a shell-in-shellarchitecture with an inner shell contained within an outer shell,according to one embodiment. In FIG. 3A, the inner shell is adapted torupture in response to application of a compressive force in order totrigger a chemiluminescent reaction within the microcapsule. In aparticular embodiment, the multiple-compartment microcapsule 300 of FIG.3A corresponds to the individual microcapsule 120 depicted in FIG. 1.

In FIG. 3A, the multi-compartment microcapsule 300 has an outer wall 301(also referred to herein as the “outer shell” of the multi-compartmentmicrocapsule 300) and contains an inner microcapsule 302 and a firstreactant 303 (or a first set of multiple reactants). The innermicrocapsule 302 has a capsule wall 304 (also referred to herein as the“inner shell” of the multi-compartment microcapsule 300) and contains asecond reactant 305 (or a second set of multiple reactants). The firstreactant(s) 303 within the multi-compartment microcapsule 300 maysurround the inner microcapsule 302, and the first reactant(s) 303 maybe prevented from contacting the second reactant(s) 305 by the capsulewall 304 of the inner microcapsule 302. The capsule wall 304 of theinner microcapsule 302 may be formed to rupture under a particularcompressive force, and the outer wall 301 of the microcapsule 300 may beformed so as to not rupture under that compressive force. Rupturing thecapsule wall 304 of the inner microcapsule 302 may allow the firstreactant(s) 303 to contact the second reactant(s) 305 and the reactantsmay then undergo a chemiluminescent reaction.

FIG. 3B is a diagram illustrating a cross-sectional view of amultiple-compartment microcapsule 310 having an inner barrier to formcompartments, according to one embodiment. In FIG. 3B, the inner barrieris adapted to rupture in response to application of a compressive forcein order to trigger a chemiluminescent reaction within the microcapsule.

In FIG. 3B, the multi-compartment microcapsule 310 has an inner barrierthat defines compartments, where the inner barrier is adapted to rupturein response to a compressive force according to some embodiments of thepresent disclosure. In FIG. 3B, the multi-compartment microcapsule 310has an outer wall 311 and contains a first reactant 313 (or a first setof multiple reactants) and a second reactant 315 (or a second set ofmultiple reactants). An inner barrier 314, which may be a membrane,within the multi-compartment microcapsule 310 may prevent the firstreactant(s) 313 and the second reactant(s) 315 from coming into contact.The inner barrier 314 may be any form of a physical barrier that formstwo or more compartments within the microcapsule 310. The inner barrier314 may be formed to rupture under a particular compressive force andthe outer wall 311 of the multi-compartment microcapsule 310 may beformed so as to not rupture under that compressive force. Rupturing theinner barrier 314 may allow the first reactant(s) 313 to contact thesecond reactant(s) 315, and the reactants may then undergo achemiluminescent reaction.

In some cases, the compressive force applied to the multiple-compartmentmicrocapsules 300 and 310 depicted in FIGS. 3A and 3B may be within arange typical of that applied in the manufacture of adhesive, polymer,or thermal interface materials. In accordance with some embodiments, theinner capsule wall 304 (of the multiple-compartment microcapsule 300shown in FIG. 3A), or the inner barrier 314 (of the multiple-compartmentmicrocapsule 310 shown in FIG. 3B), may rupture at a force no greaterthan the lower bound of this range of compressive force. The outer wall301 (of the multiple-compartment microcapsule 300 shown in FIG. 3A), orthe outer wall 311 (of the multiple-compartment microcapsule 310 shownin FIG. 3B), may sustain, without rupturing, a force no less than theupper bound of this range of compressive force.

Other embodiments may utilize more than two reactants. Themulti-compartment microcapsule 300 of FIG. 3A may contain a plurality ofinner microcapsules, such as the inner microcapsule 302, and the innermicrocapsules may themselves contain other, inner, microcapsules and/orreactants. The various microcapsules may contain reactants and mayrupture under compression to allow the reactants to come into contact.Similarly, the multi-compartment microcapsule 310 of FIG. 3B may containa plurality of compartments formed by a plurality of membranes orbarriers, such as the barrier 314, and the compartments may in turncontain one or more membranes or barriers, or may contain microcapsules.The inner shells and outer shells may contain multiple chemicals,compounds, particles, and the like. The various membranes or barriersmay rupture under compression to allow the reactants to come intocontact.

Referring to FIG. 4, a diagram 400 illustrates an example of a processof forming an electronic component cooling assembly 402 from an assemblythat includes a thermal interface material 406 (e.g., a thermal greaseor putty having light generating microcapsules dispersed therein) thatdefines an interface between a first component 408 and a secondcomponent 410.

In the particular embodiment depicted in FIG. 4, the first component 408of the electronic component cooling assembly 402 corresponds to a heatspreader that surrounds an electronic component 418 and is configured todistribute heat away from the electronic component 418 during electronicdevice operation. To illustrate, the electronic component 418 mayinclude a die, a central processing unit (CPU), a graphics processingunit (GPU), or a field programmable gate array (FPGA), among otheralternatives. The heat spreader is also referred to herein as a modulelid, and the electronic component 418 within the heat spreader is alsoreferred to herein as a lidded module. The second component 410 of theelectronic component cooling assembly 402 corresponds to a heat sink.

FIG. 4 illustrates that, during formation of the electronic componentassembly 402, a compressive force is applied to the second component 410and/or the first component 408 of the assembly. In a particularembodiment, the thermal interface material 406 of FIG. 4 corresponds tothe interface material 106 of FIG. 1. Thus, while not shown in theexample of FIG. 4, the thermal interface material 406 may include aphoto-initiator, a photo-curable material, and the microcapsules 104previously described herein with respect to FIG. 1. In FIG. 4, thecompressive force that is applied to the thermal interface material 406during formation of the electronic component assembly 402 results inrupture of the capsule wall 128 of the inner microcapsule 124, allowingthe first reactant(s) 126 and the second reactant(s) 130 to undergo achemiluminescent reaction. FIG. 4 further shows a non-limiting,illustrative example of a chemiluminescent reaction in order to showthat the light emitted from the microcapsules 104 into the thermalinterface material 406 results in the formation of a cross-linkedthermal interface material 420 between the first component 408 and thesecond component 410 of the electronic component cooling assembly 402.

The chemical reaction diagram depicted at the bottom of FIG. 4illustrates an example of a chemiluminescent reaction that occurs withinthe microcapsules 104 dispersed within the thermal interface material406 as a result of application of the compressive force during formationof the electronic component cooling assembly 402.

The top portion of the chemical reaction diagram illustrates a diphenyloxalate molecule reacting with a hydrogen peroxide molecule to form twophenol molecules and one 1,2-dioxetanedione molecule. The middle portionof the chemical reaction diagram illustrates that the 1,2-dioxetanedionemolecule, having an unstable strained ring, decomposes spontaneously tocarbon dioxide and releases energy that excites a dye (with the exciteddie identified as “dye*” in FIG. 4). The bottom portion of the chemicalreaction diagram illustrates that the excited dye then releases a photonas it returns to its ground state, with “hv” representing the standardnotation referring to release of radiant energy other than heat duringthe reaction.

The wavelength of the photon that is released as the excited dye returnsto its ground state depends on the structure of a particular dye that isselected. To illustrate, different dyes may have different photonemission spectral distributions. Similarly, different photo-initiatorsmay have different photo-initiator absorbance spectral distributions. Aphoton emission spectral distribution associated with a particular dyemay be used to identify peak emission region(s), and the peak emissionregion(s) may be compared to a photo-initiator absorbance spectraldistribution associated a particular photo-initiator to determinewhether the particular photo-initiator is sufficiently absorbent in thepeak emission region(s). As such, a particular combination of a dye anda photo-initiator may be selected such that a wavelength of a photonemitted when the excited dye returns to its original state issatisfactory to trigger the photo-initiator within the thermal interfacematerial 406 to initiate or catalyze the curing of the photo-curablematerial. In some cases, the emission peak(s) in a photon emissionspectral distribution associated with a particular dye may be comparedto a spectral distribution associated with a light source (e.g., amercury arc lamp) that is typically utilized to photo-cure apolymer/adhesive. A photo-initiator (or multiple photo-initiators) maybe identified as satisfactory for the individual emission peaks in thespectral distribution associated with the light source.

As an illustrative, non-limiting example, the dye may be9,10-diphenylanthracene which has a marked emission peak at 405 nm andappreciable emission at 436 nm. In this case, an illustrative,non-limiting example of a photo-initiator with a satisfactoryphoto-initiator absorbance spectral distribution is Ciba® IRGACURE™ 784from Ciba Specialty Chemicals Inc. It will be appreciated that numerouscombinations of dyes and photo-initiators may be suitable to cure aparticular photo-curable material.

Thus, FIG. 4 illustrates an example of a process of forming anelectronic component cooling assembly having a cross-linked thermalinterface material by applying a compressive force to an assemblyincluding a thermal interface material (having light generatingmicrocapsules dispersed therein) disposed between a heat spreader and aheat sink. FIG. 4 illustrates that application of the compressive forceto the microcapsules dispersed within the thermal interface materialcauses a chemiluminescent reaction with a photon emission wavelengththat is satisfactory to form the cross-linked thermal interfacematerial.

FIG. 5 is a flow diagram illustrating, through stages 5(a) to 5(f), anexample of a method 500 of producing a multiple-compartment microcapsulehaving a shell-in-shell architecture with an inner shell containedwithin an outer shell, where the inner shell is adapted to rupture inresponse to application of a compressive force to cause achemiluminescent reaction within the microcapsule, according to someembodiments.

In each of the stages 5(a)-5(f), the structure is shown in across-sectional side view. Referring to FIG. 5, and according to anembodiment, the shell-in-shell microcapsules can be made using anyreactants and oxidants of any chemiluminescent reaction (identified as“First Reactant(s)” and “Second Reactant(s)” in FIG. 5). For example,First Reactant(s) may be a dye and diphenyl oxalate, and SecondReactant(s) may be an oxidant such as hydrogen peroxide. Once the innershell ruptures, the reactants mix and emit photons. One skilled in theart will understand that a variety of chemiluminescent reactants can beused. Both the First Reactant(s) and the Second Reactant(s) may compriseone or more chemicals, particles, and combinations thereof.

In the example depicted in FIG. 5, magnetic nanoparticles are used inoperation 502 for incorporation into the “inner core” CaCO₃microparticles (shown at stage 5(b)). Magnetic nanoparticles areincorporated into the “inner core” CaCO₃ microparticles for the purposeof subsequently magnetically isolating the product prepared in operation506 (i.e., ball-in-ball CaCO₃ microparticles) from a coproduct (i.e.,single core CaCO₃ microparticles). The magnetic nanoparticles may be,for example, Fe₃O₄ (also referred to as “magnetite”) nanoparticles,cobalt ferrite nanoparticles or other magnetic nanoparticles known inthe art. In a particular embodiment, the magnetic nanoparticles may havea diameter in a range of approximately 6 nm to 25 nm.

An example of a technique of preparing magnetite nanoparticles follows.A 5 mol/l NaOH solution is added into a mixed solution of 0.25 mol/lferrous chloride and 0.5 mol/l ferric chloride (molar ratio 1:2) untilobtaining pH 11 at room temperature. The slurry is washed repeatedlywith distilled water. Then, the resulting magnetite nanoparticles aremagnetically separated from the supernatant and redispersed in aqueoussolution at least three times, until obtaining pH 7. A typical averagediameter of the resulting magnetite nanoparticles may be about 12 nm.

The microparticle system described with respect to FIG. 5 is based onCaCO₃ microparticles that are hardened by formation of a polyelectrolytemultilayer around the CaCO₃ microparticles. The method 500 begins bypreparing spherical calcium carbonate microparticles in which magnetitenanoparticles and First Reactant(s) (e.g., diphenyl oxalate and a dye,such as 9,10-diphenylanthracene) are immobilized by coprecipitation(operation 502). For example, 1 M CaCl₂) (0.615 mL), 1 M Na₂CO₃ (0.615mL), 1.4% (w/v) magnetite nanoparticle suspension (50 μL), FirstReactant(s) (0.50 mg dye and 133 mg oxalate), and deionized water (2.450mL) may be rapidly mixed and thoroughly agitated on a magnetic stirrerfor about 20 seconds at about room temperature. After the agitation, theprecipitate may be separated from the supernatant by centrifugation andwashed three times with water. The diameter of the CaCO₃ microparticlesproduced with a reaction time of 20 seconds is about 4 μm to about 6 μm.Smaller CaCO₃ microparticles are produced if the reaction time isreduced from about 20 seconds to about several seconds. One of theresulting CaCO₃ microparticles is shown at stage 8(b).

In this example, the fabrication of polyelectrolyte capsules is based onthe layer-by-layer (LbL) self-assembly of polyelectrolyte thin films.Such polyelectrolyte capsules are fabricated by the consecutiveadsorption of alternating layer of positively and negatively chargedpolyelectrolytes onto sacrificial colloidal templates. Calcium carbonateis but one example of a sacrificial colloidal template. One skilled inthe art will appreciate that other templates may be used in lieu of, orin addition to, calcium carbonate.

The method 500 continues by LbL coating the CaCO₃ microparticles(operation 504). In operation 504, a polyelectrolyte multilayer (PEM)build-up may be employed by adsorbing five bilayers of negative PSS(poly(sodium 4-styrenesulfonate); Mw=70 kDa) and positive PAH(poly(allylamine hydrochloride); Mw=70 kDa) (2 mg/mL in 0.5 M NaCl) byusing the layer-by-layer assembly protocol. For example, the CaCO₃microparticles produced in operation 502 may be dispersed in a 0.5 MNaCl solution with 2 mg/mL PSS (i.e., polyanion) and shaken continuouslyfor 10 min. The excess polyanion may be removed by centrifugation andwashing with deionized water. Then, 1 mL of 0.5 M NaCl solutioncontaining 2 mg/mL PAH (i.e., polycation) may be added and shakencontinuously for 10 min. The excess polycation may be removed bycentrifugation and washing with deionized water. This deposition processof oppositely charged polyelectrolyte may be repeated five times and,consequently, five PSS/PAH bilayers are deposited on the surface of theCaCO₃ microparticles. One of the resulting polymer coated CaCO₃microparticles is shown at stage 5(c).

The thickness of this “inner shell” polyelectrolyte multilayer may bevaried by changing the number of bilayers. Generally, it is desirablefor the inner shell to rupture while the outer shell remains intact sothat the reactants and the reaction products do not contaminate theinterface material (e.g., an adhesive, a thermal interface material,etc.) into which the multi-compartment microcapsule may be dispersed.Typically, for a given shell diameter, thinner shells rupture morereadily than thicker shells. Hence, in accordance with some embodimentsof the present disclosure, the inner shell is made relatively thincompared to the outer shell. On the other hand, the inner shell must notbe so thin as to rupture prematurely.

The PSS/PAH-multilayer in operation 504 is but one example of apolyelectrolyte multilayer. One skilled in the art will appreciate thatother polyelectrolyte multilayers and other coatings may be used in lieuof, or in addition to, the PSS/PAH-multilayer in operation 504.

The method 500 continues by preparing ball-in-ball calcium carbonatemicroparticles in which Second Reactant(s) (which can be any suitableoxidant, including hydrogen peroxide) is immobilized by a secondcoprecipitation (operation 506). “Immobilize” means “removing fromgeneral circulation, for example by enclosing in a capsule.” Theball-in-ball CaCO₃ microparticles are characterized by a polyelectrolytemultilayer that is sandwiched between two calcium carbonatecompartments. In operation 506, the polymer coated CaCO₃ microparticlesmay be resuspended in 1M CaCl₂ (0.615 mL), 1M Na₂CO₃ (0.615 mL), anddeionized water (2.500 mL) containing hydrogen peroxide (1 mg), rapidlymixed and thoroughly agitated on a magnetic stirrer for about 20 secondsat about room temperature. After the agitation, the precipitate may beseparated from the supernatant by centrifugation and washed three timeswith water. The second coprecipitation is accompanied by formation of acoproduct, i.e., single core CaCO₃ microparticles that contain onlyhydrogen peroxide. Hence, the resulting precipitate represents a mixtureof ball-in-ball CaCO₃ microparticles and single core CaCO₃microparticles. The ball-in-ball CaCO₃ microparticles, which aremagnetic due to the immobilized magnetite nanoparticles in the innercompartment, may be isolated by applying an external magnetic field tothe sample while all of the nonmagnetic single core CaCO₃ microparticlesare removed by a few washing steps. One of the resulting ball-in-ballCaCO₃ microparticles is shown at stage 5(d).

In an embodiment, the outer shell wall material is made of a materialfor the chemiluminescent photon to escape the shell. In anotherembodiment, the outer shell wall material is made of a material wherethe photon yield outside the wall of the outer shell wall is maximized.In an embodiment, the outer shell wall has a transmittance of at least90%. In certain embodiments, the outer shell wall material may includenatural polymeric material, such as gelatin, arabic gum, shellac, lac,starch, dextrin, wax, rosin, sodium alginate, zein, and the like;semi-synthetic polymer material, such as methyl cellulose, ethylcellulose, carboxymethyl cellulose, hydroxyethyl ethyl cellulose;full-synthetic polymer material, such as polyolefins, polystyrenes,polyethers, polyureas, polyethylene glycol, polyamide, polyurethane,polyacrylate, epoxy resins, among others. In certain embodiments, themethod for wrapping a core material includes chemical methods such asinterfacial polymerization, in situ polymerization, molecularencapsulation, radiation encapsulation; physicochemical methods such asaqueous phase separation, oil phase separation, capsule-heart exchange,pressing, piercing, powder bed method; and physical methods, such asspray drying, spray freezing, air suspension, vacuum evaporationdeposition, complex coacervation, long and short centrifugation.

An example of a conventional technique of preparing the outer shellfollows, and can be accomplished at stage 5(e). A gelatin is dissolvedinto n-hexane in a water bath at about 50° C. to obtain a 6% gelatinsolution. The gelatin may optionally be swelled with deionized waterbefore the preparation of the gelatin solution. The ball-in-ball CaCO₃microparticles prepared in operation 506 are added to the gelatinsolution while stirring to form an emulsified dispersion system. The pHis then adjusted to about 3.5-3.8 using acetic acid, and then a 20%sodium sulfate solution is slowly added into the dispersion system whilemaintaining a temperature of about 50° C. The temperature of thedispersion system is then lowered to a temperature of about 15° C. Theresult is a colloid of gelatin coated ball-in-ball CaCO₃ microparticles.

Generally, it is desirable for the inner shell to rupture while theouter shell remains intact so that the reactants and the reactionproducts do not contaminate the sealant or adhesive into which themulti-compartment microcapsule is dispersed. Typically, for a givenshell diameter, thinner shells rupture more readily than thicker shells.Hence, in accordance with some embodiments of the present disclosure,the outer shell is made relatively thick compared to the inner shell.

Operation 510 is a CaCO₃ extraction. In operation 510, the CaCO₃ core ofthe ball-in-ball CaCO₃ microparticles may be removed by complexationwith ethylenediaminetetraacetic acid (EDTA) (0.2 M, pH 7.5) leading toformation of shell-in-shell microcapsules. For example, the gelatincoated ball-in-ball CaCO₃ microparticles produced in operation 508 maybe dispersed in 10 mL of the EDTA solution (0.2 M, pH 7.5) and shakenfor about 4 h, followed by centrifugation and re-dispersion in freshEDTA solution. This core-removing process may be repeated several timesto completely remove the CaCO₃ core. The size of the resultingshell-in-shell microcapsules ranges from about 8 μm to about 10 μm, andthe inner core diameter ranges from about 3 μm to about 5 μm. One of theresulting shell-in-shell microcapsules is shown at stage 5(f). Dependingon the application of use, the shell-in-shell microcapsule can have arange of about 0.5 μm to about 200 μm.

As noted above, the fabrication of polyelectrolyte capsules in themethod 500 of FIG. 5 is based on the layer-by-layer (LbL) self-assemblyof polyelectrolyte thin films. One skilled in the art will appreciatethat a multi-compartment microcapsule for photon generation inaccordance with some embodiments of the present disclosure may beproduced by other conventional multi-compartment systems, such aspolymeric micelles, hybrid polymer microspheres, and two-compartmentvesicles.

As noted above, one skilled in the art will understand that variouschemiluminescent reactants and oxidants can be used. Moreover, themulti-compartment microcapsule can utilize various chemiluminescentreactions. The chemistry used in chemiluminescent reactions is a maturetechnology, and those skilled in the art will know that additionalmaterials can be further added to the multi-compartment microcapsule.For example, enhancing reagents such as alkyl dimethyl benzyl quaternaryammonium salt may be added to the reactants.

While the method 500 of FIG. 5 illustrates formation of shell-in-shellmicrocapsules where the inner shell is adapted to rupture in response toa compressive force, the inner shell can be adapted to rupture inresponse to other forms of stimuli including heat and ultrasound.

Other embodiments may utilize more than two reactants. For example, themulti-compartment microcapsule 300 of FIG. 3A may contain a plurality ofinner microcapsules, such as 304, and the inner microcapsules maythemselves contain other, inner, microcapsules. The variousmicrocapsules may contain reactants and may rupture under compression toallow the reactants to come into contact. Similarly, themulti-compartment microcapsule 310 of FIG. 3B may contain a plurality ofcompartments formed by a plurality of membranes or barriers, such as314, and the compartments may in turn contain one or more membranes orbarriers, or may contain microcapsules. The various membranes orbarriers may rupture under compression to allow the reactants to comeinto contact. For example, one inner shell microcapsule containsreactants (A), and second inner microcapsule contains reactants (B), andthe outer shell microcapsule contains reactants (C). Depending on thestrength of the stimuli (i.e., compression), inner shell containingreactants (A) will rupture, while inner shell containing reactants (B)will not rupture.

Other embodiments may utilize more than one multi-compartmentmicrocapsule, where the individual multi-compartment microcapsules havedifferent strengths in response to a stimulus (e.g., compressive force,a magnetic field, ultrasound, heat, or combinations thereof). Forexample, one multi-compartment microcapsule may have an inner shellcontaining reactants (A), and the outer shell containing reactants (B).The other multi-compartment microcapsule may have an inner shellcontaining reactants (C) and the outer shell containing reactants (D).In this embodiment, multiple emission bands can be achieved depending onthe strength of the applied stimulus. Emission 1 would comprise thechemiluminescent reaction of reactants (A) and (B) after a stimuliruptures the inner shell of one microcapsule, while emission 2 wouldcomprise the chemiluminescent reaction of (C) and (D) after a stimuliruptures the inner shell of the other microcapsule.

The photon-emitting reactants may be chosen to be inert with respect tothe material of the microcapsule walls, or an isolating barrier within amicrocapsule when the reactants are not in contact. The photon-emittingreactants also may be chosen to be inert with respect to the outermicrocapsule wall when the reactants are in contact, or such that thechemical products of the reaction are inert with respect to the outermicrocapsule wall, and any remnants of the inner microcapsule wall orbarrier.

An amount of the first reactant and an amount of the second reactant maybe determined. The amounts may be determined from the total amount ofthe reactants required to produce a desired amount of photons, the ratioof each reactant according to a reaction equation, the desireddimensions of the microcapsule, and the manner of isolating thereactants within the capsule. For example, a microcapsule may be desiredhaving a maximum dimension less than or equal to a desired finalthickness of less than 0.5 microns, and the amount of reactants may bechosen corresponding to the volume available within a microcapsuleformed according to that dimension.

One or more inner microcapsules, such as illustrated by microcapsule 300of FIG. 3A, may be formed and the inner microcapsules may contain secondreactant(s). In various embodiments, an inner microcapsule may be formedto contain chemiluminescent reactants (including dye, oxalates, otherreactants described herein, and combinations thereof). The innermicrocapsule(s) may be formed with a capsule wall configured to rupturewith application of a compressive force.

Further, an outer microcapsule may be formed containing the innermicrocapsule(s) and one or more other reactants, in the manner ofmulti-compartment microcapsule 300 in FIG. 3A. The reactant(s) containedin the outer microcapsule may be inert with respect to each other andthe microcapsule walls until in contact with one or more reactantscontained in one or more inner microcapsules. In one embodiment, anouter microcapsule may contain hydrogen peroxide, or other oxidizers,where one or more inner microcapsules contain chemiluminescent reactants(including dye, oxalates, etc.). The capsule wall of the outermicrocapsule may be formed to not rupture at the compressive forceapplied to rupture the capsule wall of the inner microcapsule.

Alternatively, an embodiment may utilize a microcapsule having astructure as illustrated by the multi-compartment microcapsule 310 inFIG. 3B. In accordance with this alternative embodiment, an outermicrocapsule may be formed having one or more inner barriers 314, whichmay be membranes, in the manner of the multi-compartment microcapsule310 in FIG. 3B, forming two (or more) compartments within the outermicrocapsule. The particular reactants described above may be containedwithin the compartments, and the inner barrier(s) may be formed torupture at compressive forces such as described above with respect tothe capsule wall of an inner microcapsule.

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

What is claimed is:
 1. A process of curing a photo-curable material, theprocess comprising: dispersing a microcapsule in a material thatincludes a photo-initiator and a photo-curable material; and applying astimulus to the microcapsule to trigger a chemiluminescent reactionwithin the microcapsule, the chemiluminescent reaction generating aphoton having a wavelength within a particular emission range that isconsistent with an absorption range of the photo-initiator, wherein thephoton exits the microcapsule to trigger the photo-initiator to initiateor catalyze curing of the photo-curable material.
 2. The process ofclaim 1, wherein the chemiluminescent reaction includes excitation of adye from a ground state to an excited state and subsequent release ofthe photon upon relaxation from the excited state to the ground state.3. The process of claim 2, wherein excitation of the dye is caused byenergy released during decomposition of a 1,2-dioxetanedione molecule.4. The process of claim 3, wherein a chemical reaction of a diphenyloxalate molecule with a hydrogen peroxide molecule results in formationof the 1,2-dioxetanedione molecule.
 5. The process of claim 2, whereinthe dye includes 9,10-diphenylanthracene.
 6. The process of claim 1,wherein the material includes a thermal interface material or anadhesive.
 7. The process of claim 1, further comprising: disposing thematerial between a first component and a second component to form anassembly; and applying the stimulus to the microcapsule by applying acompressive force to the assembly.
 8. The process of claim 7, wherein:the material includes a thermal interface material; the first componentincludes a heat spreader surrounding an electronic component thatgenerates heat during operation; the second component includes a heatsink; and compression of the assembly results in formation of anelectronic component cooling assembly having a cross-linked thermalinterface material disposed between the heat spreader and the heat sink.9. The process of claim 1, wherein the microcapsule includes amultiple-compartment microcapsule that comprises: a first compartmentthat contains a first reactant; a second compartment that contains asecond reactant; and an isolating structure separating the firstcompartment from the second compartment, the isolating structure adaptedto rupture in response to the stimulus to cause the first reactant andthe second reactant to undergo the chemiluminescent reaction.
 10. Theprocess of claim 9, wherein the multiple-compartment microcapsuleincudes a shell-in-shell microcapsule comprising an inner shellcontained within an outer shell, wherein the inner shell encapsulatesthe first compartment, wherein the outer shell encapsulates the secondcompartment, and wherein the inner shell defines the isolatingstructure.
 11. The process of claim 10, wherein the outer shellcomprises a polymer, and the outer shell has a transmittance value of atleast 90% for the wavelength within the particular emission range. 12.The process of claim 11, wherein the polymer comprises gelatin, arabicgum, shellac, lac, starch, dextrin, wax, rosin, sodium alginate, zein,methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethylethyl cellulose, polyolefins, polystyrenes, polyethers, polyesters,polyureas, polyethylene glycol, polyamides, polyimides,urea-formaldehydes, polyurethane, polyacrylate, epoxy resins, andcombinations thereof.
 13. An in-situ photo-curing process comprising:forming an assembly that includes a material disposed between a firstcomponent and a second component, the material including aphoto-initiator, a photo-curable material, and microcapsules dispersedtherein; and applying a stimulus to the assembly, wherein the stimulustriggers chemiluminescent reactions within the microcapsules, thechemiluminescent reactions generating photons having wavelengths withina particular emission range that is consistent with an absorption rangeof the photo-initiator, wherein the photons exit the microcapsules forin-situ curing of the photo-curable material.
 14. The in-situphoto-curing process of claim 13, wherein: the material includes athermal interface material; the first component includes a heat spreadersurrounding an electronic component that generates heat duringoperation; the second component includes a heat sink; and compression ofthe assembly results in formation of an electronic component coolingassembly having a cross-linked thermal interface material disposedbetween the heat spreader and the heat sink.
 15. The in-situphoto-curing process of claim 14, further comprising forming the thermalinterface material by dispersing the microcapsules in a thermal greaseor putty.
 16. The in-situ photo-curing process of claim 13, wherein themicrocapsules include an outer wall having a transmittance value of atleast 90% for the wavelengths within the particular emission range. 17.A material comprising: a photo-initiator; a photo-curable material; amicrocapsule that includes: a first compartment that contains a firstreactant; a second compartment that contains a second reactant; and anisolating structure separating the first compartment from the secondcompartment, the isolating structure adapted to rupture in response toapplication of a stimulus to cause the first reactant and the secondreactant to undergo a chemiluminescent reaction, wherein thechemiluminescent reaction generates a photon having a wavelength withina particular emission range that is consistent with an absorption rangeof the photo-initiator, and wherein the photon exits the microcapsule totrigger the photo-initiator to initiate or catalyze curing of thephoto-curable material.
 18. The material of claim 17, wherein thestimulus includes a compressive force, heat, or a combination thereof.19. The material of claim 17, wherein the microcapsule further comprisesan outer shell and wherein the outer shell has a transmittance value ofat least 90% for the wavelength within the particular emission range.20. The material of claim 19, wherein the outer shell comprises gelatin,arabic gum, shellac, lac, starch, dextrin, wax, rosin, sodium alginate,zein, methyl cellulose, ethyl cellulose, carboxymethyl cellulose,hydroxyethyl ethyl cellulose, polyolefins, polystyrenes, polyethers,polyesters, polyureas, polyethylene glycol, polyamides, polyimides,urea-formaldehydes, polyurethane, polyacrylate, epoxy resins, andcombinations thereof.